This invention relates to an AC capacitor containing as its impregnant system a dielectric fluid containing an aliphatic or aromatic isocyanate to improve the life characteristics of the capacitor.
For quite a while, dielectric fluid impregnated capacitors used polychlorinated biphenyls or PCB's. Environmental concerns have caused a reduction in their usage, and non-halogenated organic liquids are being used more frequently. Some of these non-halogenated materials are ester-based fluids, frequently stabilized by epoxides. Even if these liquids are stabilized, e.g., against hydrolysis, metallized AC capacitors impregnated with them show a capacitance loss on life testing. This loss may be caused by corona, traces of water or acids, or incomplete impregnation of wound sections.